Because of increasing concern about global environmental problems, the utilization of various fuel cells has been studied recently. Among these, in a case of a solid oxide fuel cell having a high efficiency, a hydrogen-rich gas is supplied as a fuel gas, and power is generated by an electrochemical reaction of oxygen used as an oxidant with hydrogen, carbon monoxide, and hydrocarbons.
Moreover, for the fuel gas, a method may be adopted which supplies a reformed gas obtained by reforming a liquid fuel. In such reforming, a high-carbon organic liquid including gasoline is vaporized and gasified or a fuel gas is used as a reforming fuel. The reforming is performed by introducing the reforming fuel into a reformer together with other components necessary for the reforming reaction. In this event, the reforming fuel is reformed with a reforming catalyst in the reformer. Since the reforming reaction requires heat, it is important to widely supply the whole area of the reforming catalyst with heat in a right amount without excess and deficiency.
Hence, there have been conventionally proposed reformers having a structure, in which a combustion layer and a reforming layer are separated. Patent Literature 1 discloses an example of such reformers. In the reformer disclosed in Patent Literature 1, a combustion passage and a reforming passage are disposed with a wall therebetween, and a combustion gas supplied to the combustion passage is combusted on a combustion catalyst to generate heat. This heat is conducted to a reforming catalyst in the reforming passage for a reforming reaction in the reforming layer.
Conventionally, in such a reformer, one of simplest ways of supplying a combustion gas is that a to-be-combusted gas and a combustion-assisting gas are mixed together in advance at the outside and are supplied as the combustion gas to the reformer. Nevertheless, in this method, occurrence of an exothermic reaction is localized near an inlet of the combustion passage. This brings about problems that a sufficient amount of heat is not obtained on a downstream side of the combustion passage, and a reforming reaction does not take place sufficiently there.
For this reason, in the reformer disclosed in Patent Literature 1, a to-be-combusted gas is introduced separately from a combustion-assisting gas by using a pipe to a site where heat is desired to be generated in the combustion passage, so that an exothermic reaction takes place on the entire combustion catalyst.